Radiative transition dynamics of holmium ions-doped LaF3 nanocrystals

Abstract

Ho3+-doped LaF3 nanocrystals with 1.0, 3.0, and 5.0 mol% Ho3+ have been prepared by hydrothermal method. The nanocrystals possess hexagonal structure with $$P\stackrel{-}{3}c1$$ space group with lattice parameters a = 7.172 ± 0.002 A and c = 7.342 ± 0.002 A. The room temperature absorption, luminescence spectra of LaF3:Ho3+ was investigated in detail. Judd–Ofelt theory has been applied to estimate $${{\Omega }}_{{\uplambda }}$$ (λ = 2, 4, 6) intensity parameters. For LaF3:5%Ho3+ sample, $${\varOmega }_{2}=1.872\times {10}^{-20}{\text{cm}}^{2},$$ $${\varOmega }_{4}=4.006\times {10}^{-20}{\text{cm}}^{2}$$ and $${\varOmega }_{6}=4.720\times {10}^{-20}{\text{cm}}^{2}.$$ Based on these Judd–Ofelt parameters, various radiative parameters such as radiative transition probabilities $${ A}_{R},$$ radiative lifetime $${ \tau }_{R},$$ branching ratios $${\beta }_{R}$$ and stimulated emission cross-section $${\sigma }_{em}\left({\lambda }_{p}\right)$$ for various emission levels of LaF3:5%Ho3+ sample have been determined. It is found that the luminescence quantum efficiency of 5F5 excited state is decreased from 55.8 to 37.9% with increasing Ho3+ concentration from 1 to 5 mol%.